This sporadic event is the biggest natural influence on year-to-year weather and adds a further spurt of warmth to an already overheating world. The result is supercharged extreme weather, hitting lives and livelihoods.
The last major El Niño, from 2014 to 2016, led to each of those years successively breaking the global temperature record, and 2016 remains the hottest year ever recorded. However, this El Niño has now begun and may already be driving new temperature records, with record heatwaves on land from Puerto Rico to China and record heatwaves in the seas around the UK.
What is the El Niño-La Niña cycle?
Variations in wind strength and ocean temperatures in the vast Pacific Ocean lead to two distinct climate patterns, El Niño and La Niña. The switch between them happens irregularly, every 3-7 years, usually with neutral years in between. El Niños tend to last about a year but the La Niña phase can be longer, and 2023 has seen the end of an unusual run of three successive La Niña years.
What drives the cycle?
Easterly winds normally push warm surface waters in the equatorial Pacific towards Australia and Indonesia and away from South America. As a result, warm water piles up in the west Pacific and cool water is drawn up from depth in the east Pacific. This is the neutral state.
But at the onset of El Niño, the easterly winds weaken and the warm water spreads back across the whole Pacific. In contrast, at the onset of La Niña, the easterly winds are even stronger than normal, leading to further cooling of the east Pacific waters.
The erratic timing of the switches between neutral, El Niño and La Niña conditions are the result of complex interactions between different phenomena, from ocean current dynamics to thunderstorm cloud formation.
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Denne historien er fra June 24, 2023-utgaven av The Guardian.
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